I have a lawnmower blenny and a mean clean-up crew...seems to do fine job. QS has a much bigger tank than I and he only has one, so I think it could definatly make a dent in it. I use ro/di as well. Is the green stuff hard, cuz I had some hard green stuff that turned into purple corraline much to my relief. I wouldn't cut back anymore than what you already are with the lights, from what I hear that does more harm than good. What do you have in your sump? Any macro algae or mangroves?